BAS-204 Visual Aid Library
Figure-use rule
Each figure is an orientation and reasoning aid, not a project drawing. Learners must pair it with the current sequence, point list, wiring/piping documents, manufacturer instructions, and as-found evidence.
Normal-rule anchor
A point name is not a complete installation and a precise sensor in the wrong location reports the wrong process accurately.
Case overlay
A duct-static point omits pickup/range while a space sensor is above heat-producing equipment and a generic device is on hand.
Calculation/evidence callout: Reconcile point/device/location/interface fields and calculate supplied placement/averaging and expected-bias bounds.
Normal-rule anchor
Sensor range, technology, placement, enclosure, power, signal, calibration, and use all matter; displayed plausibility is not accuracy proof.
Case overlay
A CO2 sensor has no warm-up record and a duct averaging element is coiled instead of distributed across the duct.
Calculation/evidence callout: Convert supplied signal/resistance to engineering units, calculate offset/error, and compare response/freshness to criteria.
Normal-rule anchor
The transmitter cannot correct a poor pickup, reversed ports, blocked/kinked/wet tubing, wrong range, or invalid flow profile.
Case overlay
A hybrid VVT zone uses an aftermarket crossflow pickup, but tubing is reversed and the sensor range masks low airflow.
Calculation/evidence callout: Calculate differential-pressure/airflow relationships from supplied constants, range utilization, zero offset, and expected direction.
Normal-rule anchor
Safety/protective devices are not ordinary comfort points; exact approved sequence, listing, responsible authority, and impairment/restoration controls govern.
Case overlay
A low-limit capillary protects only one corner of a large coil and a student proposes bypassing it to finish a fan test.
Calculation/evidence callout: Calculate supplied coverage/spacing and response requirements; no score compensates for unsafe bypass or unowned reset.
Normal-rule anchor
Actuator percentage is not blade position, and blade position is not airflow; mechanics and process evidence remain separate.
Case overlay
The actuator reaches 100%, but linkage slips and outside-air blades remain partly closed.
Calculation/evidence callout: Calculate required torque from supplied design, command/feedback deviation, stroke time, and process-response acceptance.
Normal-rule anchor
Valve selection and piping are design/trade work; BAS installers verify approved model, orientation, actuator, signal, stroke, and evidence without inventing hydronic design.
Case overlay
A valve is installed against flow arrow and reaches full command without expected discharge-temperature change.
Calculation/evidence callout: Calculate supplied Cv/flow or design comparison, stroke/feedback, temperature change, and authority limitation without overclaiming cause.
Normal-rule anchor
An interposing relay belongs in the approved control circuit, never one phase of a motor power circuit; contact labels and normal state must be traced.
Case overlay
A RIB relay is wired on one leg of a three-phase starter and a current switch threshold falsely proves a stopped motor.
Calculation/evidence callout: Calculate coil/contact/interface load from supplied ratings and compare proof threshold/current to normal operating evidence.
Normal-rule anchor
A good physical placement cannot overcome wrong power, reference, terminal, input mode, scale, or database mapping.
Case overlay
A 4-20 mA transmitter is wired as a 0-10 V input and shares an incompatible reference with another device.
Calculation/evidence callout: Calculate expected signals and scaling endpoints/midpoint; trace loop power and voltage burden from supplied data.
Normal-rule anchor
Device checkout proceeds from identity and physical installation to signal/object and process; changing software cannot repair every defect.
Case overlay
Three devices show plausible BAS values, but one is badly located, one has reversed tubing, and one is held by an override.
Calculation/evidence callout: Reconcile inspected/pass/fail/corrected/retested points and quantify deviation, response, and remaining uncertainty.
Normal-rule anchor
A device is not handed off until another professional can find it, understand its interfaces and limitations, reproduce evidence, and know open ownership.
Case overlay
Ceilings close while an averaging sensor route, two device tags, and a failed actuator-travel test remain undocumented.
Calculation/evidence callout: Calculate artifact/point completeness and reconcile all installed/tested/corrected/as-built counts before release.